1. Field of the Invention
The present invention refers to a seal ring of a mechanical seal assembly. Particularly, the invention refers to a seal ring with a base body of silicon carbide, silicon nitride, metal or tungsten carbide or carbon fiber composite material, wherein a special slide layer is formed on at least one of the faces, said slide layer qualifying the said face as a slide surface. To make the seal ring runnable, the distortion of the base body caused by the coating of the running surface of the seal ring with slide material is set by way of the targeted coating of the rear side of the base body. Owing to the special thickness and configuration of the slide layer and the coating defined relative thereto of the opposite side of the seal ring, a much longer running time of the seal is made possible. Furthermore, the present invention refers to a method for producing such a seal ring.
2. Description of Related Art
The prior art discloses mechanical seals in many different configurations, the seal rings being subjected during operation to extremely high loads that always lead to wear of the slide surfaces down to the base body. Therefore, the use of seal rings with slide surfaces based on carbon has gained importance. Owing to this carbon surface coating the mechanical seals can be used at high temperatures, but also under conditions with great temperature changes and simultaneously at great mechanical loads.
The coatings show a high resistance to wear and have excellent dry-running properties, the resistance, however, decreasing upon mechanical damage to the coating and necessitating an exchange of the seal rings. To achieve a resistance of the seal rings to damage that is as high as possible, these must be configured to be as flat as possible and the opposite ring surfaces must be formed very plane-parallel.
Furthermore, a configuration of the slide layer with a great thickness, if possible, independently of the material and under otherwise constant good adhesion and wear characteristics, has a positive effect on the damage behavior because more wear material is available and the running time of the seal is thereby prolonged considerably.
To improve the wear resistance, it is known from DE 199 22 665 that a three-dimensional body is coated with fine-crystalline diamond, which body may be configured as a seal ring and has a base body made of SiC.
Moreover, it has been suggested in the prior art in DE 20 2006 006 425 that the base body of a seal ring is provided with an additional substrate layer between base body and diamond layer.
Furthermore, DE 20 2007 016 868 discloses a seal ring in which diamond particles are introduced as additional material into the base body consisting of a two-component material. As a result, the coating consisting of a diamond-containing material is anchored at the base body in an improved way.
It is true that diamond coatings with an inherently high strength have the advantage that they make the correspondingly coated slide body more resistant to thermally and mechanically caused stresses or stress variations. In general, however, there is the drawback that it is difficult to produce them with the maximum quality required for mechanical seals, that they require an extremely high quality test rate and that they are extremely expensive on account of the coating material and also because of the quality control and that their use requires precise calculations.
Apart from the cost-specific drawbacks, the high coating temperatures of about 700° C. which are typical of diamond coatings present problems. During the coating process and in response to the thermal expansion coefficient of the base body to be respectively coated, these temperatures cause distortions and irregularities on the base body that in cooperation with the slide pairs have a negative effect in the seal.
Therefore, SiC rings have so far preferably been coated because the thermal expansion coefficients of SiC with about 4*10−6/K and of the diamond coating with about 1*10−6/K are relatively similar at room temperature and converge further when the temperature is raised.
A further possibility of providing rings with slide-improving properties is surface coating with the so-called DLC or also “diamond like carbon” layers.
DE 38 20 581 is e.g. known from the prior art; it starts from a thickness of the DLC layer on the seal ring of up to 10 μm.
US 2010/0061676 describes a mechanical seal to be used in ultrapure water, which specifies a DLC layer thickness of at least 1 μm, but not more than 5 μm.
On the whole, the coating of slide bodies with hydrocarbon layers is described in general and specifically with DLC layers and constitutes prior art.
And although this coating is represented as prior art, relatively thick hydrocarbon layers on slide bodies pose great problems. It is known from practice that great layer thicknesses always cause problems because relatively thick DLC layers create increased stresses. Like in the case of layer systems, these may in general occur only in the base body, only in the coating, preferably between base body and coating or in a different form in all of the said regions at the same time.
Moreover, all publications have in common that only one surface of the seal ring is qualified as a slide surface. Since in all coating processes the ring to be coated rests on a surface, only one side of the ring is in general coated. This creates a relatively small layer thickness because in the coating process with hydrocarbon layers the base body is heated, which causes distortions of the ring.